The speakers are really quite different and serve different purposes. First thing you have to decide is which amp you are most likely to drive them with. I know nothing about the Darling amp but I am going to assume that it does not fair well into 4 ohm loads. I really don't know much about the Dynaco either, but if you are using the ST-30 amp, power really isn't an issue.

Lets assume either amp can properly drive the MKII, then it really boils down to efficiency vs. smoothness. The HDT is a very efficient speaker. I run an EL34 amp in triode that puts out about 4 watts max and can get it very loud. I believe part of this perceived loudness is the midrange presence from the speaker as well.

The MKII on the other hand is going to be a smoother speaker and more forgiving. It also will give you more bottom end weight and better imaging.

I am going to assume you want to use your 1.5 watt SET so I am going to recommend the HDT using the single Fostex driver. The impedance match is better suited for your amp and you are really going to appreciate that extra efficiency. 1.5 watts is not alot of power and 2 db more efficiency can mean the difference between you being able to hit an unrestricted listening level or longing for a bit more...

Probably my favorite characteristic of a good hi-fi SET is the midrange bloom available. I suspect the Fostex HDT also potrays this bloom more realistically, or put another way, doesn't smooth it over.

You did not mention whether the ribbon tweeters you have are from Decware or not. I am assuming they are not. With all do respect but I believe Steve modifies these tweeters and I chance to say your's may be inferior to what is recommended. If you are going to go through the trouble of building an HDT cabinet then you might as well use the exact drivers he uses in the tweaked design.

Considering the Fostex driver, all you have to do there is cut away the dust cap and install a 15/16 inch socket to the pole piece, done.

For my own personal tastes, and now that I have an amp with tube rectifiers and a really smooth top end from choice resistors and caps, I would not be without the midrange presence and bloom offered by the HDT with the Fostex. The HDT will make things sound scary real, especially voice, it is right in your room with you and that is always great.

I just installed the mkII drivers in my HDT cabinets after listening to the fostex drivers for about 1.5 years. I like this setup too, but it's a quite different animal.

Both are good. I won't even begin to comment beyond that since these haven't had any break in time.

If you are running a single C, CS or similar low watt amp, I'd recommend the Mk I with the fostex driver because of efficiency. While 1 amp would be sufficient in a small room, I run 2 bridged cs's to get the volume I'm accustomed to with the fostex drivers. This may change as things open up over time.

Nope Rappy,The double plate design is the original Steve Deckert design.Looking down at the top of an HDT with no plate on top there is a trianglular exit of the transmission line section at the back of the top. (BTW I know you know this but just want to be complete in my description)The lower plate on the MkII has a diamond shape cutout that is situated above the opening. Then the top plate is solid above that. Both plates have the same semicircle cutout at the front. All this conspires to create a diffraction/reflection of sound exiting the top opening and along with the passives and front firing drivers give the speaker a radial dipersion of sorts, though I'm certain not all the frequencies are being represented in similar measure on any given side of the entire unit. I'm sure it improves imaging and sound stage. Just plain vanilla forward firing FE206E sucks as far as depth goes. Width always seems to happen for single full range drivers but I much prefer some mids and lows being cast out and around to the back. I have never had back wall reflections hurt the focus of images as LONG AS the reflected sound is very diffuse.

I am only using one plate at the moment, but plan to go to the woodshop to make the lower plate with the notch in the back...one of the reasons I am only at mk1.75.

When pondering this experiment, I talked through the design differences between the MkI vs MkII diffusers with Steve Deckert. The other reason that I'm still at 1.75 is that my cabinets, except for some beveling at the face plate and chamfering at the edges are still bare nekked. Since this is my favorite set of speakers in the past 20 years (with either driver configuration), I may have to do something about a long lasting finish in the near future! (actually, I couldn't wait to hear them in either setup, and couldn't bear to take them away once I did)...for now, it matches the bare MDF wall shelving and other projects around.

I've really been enjoying the Mk II setup for the past month, but I'm glad that I have 2 selects in monoblock setup to power them. 1 works fine, but 2 are nice for more extension and volume.

At first I used Solen caps on the tweeter, but changed to Sonicaps last week. These have a much more open sound. The more the drivers break in, the faster and more transparent they seem to get. I was initially concerned because in some bass and midrange they seemed soft in comparison to the 206e's. This is much less of a concern now as the sound is becoming crisper in the regions that sounded less defined.

Just a thought, since i run monblocked CS amps, the load the amp sees from each speaker is 2 ohms nominally with the xformers in series, and may be the cause for my impression that some of the mid and bass being less detailed than the FE206e driver (which I ran from a single stereo CS seeing 8 ohms). Will do some listening tests with series monoblock, parallel monoblock and single stereo amplifier.

if the HDT2's are 4 ohm nominally, what is the effective impedance when the xformers are connected in parallel monoblock mode?